| ( | 21 | − | 2 | x | ) | ( | 27 | − | 2 | x | ) | = | 1 | ÷ | 4 | × | 27 | × | 21 |
| Left side of the equation = | 21 | ( | 27 | − | 2 | x | ) | − | 2 | x | ( | 27 | − | 2 | x | ) |
| = | 21 | × | 27 | − | 21 | × | 2 | x | − | 2 | x | ( | 27 | − | 2 | x | ) |
| = | 567 | − | 42 | x | − | 2 | x | ( | 27 | − | 2 | x | ) |
| = | 567 | − | 42 | x | − | 2 | x | × | 27 | + | 2 | x | × | 2 | x |
| = | 567 | − | 42 | x | − | 54 | x | + | 4 | x | x |
| = | 567 | − | 96 | x | + | 4 | x | x |
| 567 | − | 96 | x | + | 4 | x | x | = | 1 | ÷ | 4 | × | 27 | × | 21 |
| Right side of the equation = | 567 4 |
| 567 | − | 96 | x | + | 4 | x | x | = | 567 4 |